US 3473027 A
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Description (OCR text may contain errors)
Oct. 14. 1969 FREEMAN ET AL 3.473,027
PROCESS FoR RECORDING AND RETRIEVING lNFORMATION EMPLOYING PHOTOLUMINESCENT INKS WHICH LUMINESCE UNDER ULTRAVIOLET ILLUMINATION Filed Oct. 14, 1966 PH 0 7'0 TUBE S D/SPERS/NG a 3 L ELEMENT 1 I- 4-APER TURE uv L/IGHT SOURCE QUARTZ READ/N6 SURFACE CHARACTER 1.\\' EATORS.
BE/N6 READ MARK PH/LL/PS FREEMAN FEEDER/CK HALVERSO/V BY 7 We M4 32.
ATTORNEY United States Patent Int. Cl. G01n 21/38 US. Cl. 250-71 14 Claims ABSTRACT OF THE DISCLOSURE A process is disclosed of recording information and retrieving .it which comprises forming symbols of inks having one or more photoluminescent components which luminesce under ultraviolet or other short wave illumination in at least one wavelength band substantially different from that of any other luminescent component. The code consists in the presence in one or more concentrations or absence of the photoluminescent components. Preferably, the code is represented by the presence or absence of components and permits a choice of 2l symbols, where n is the number of components. Preferably, at least one or more of the components are narrow bands fiuorescers which involve complexes, such as chelates, of lanthanide ions having an atomic number greater than 57, which are all materials which luminesce in -very narrow Wavelength bands. The coded inks can be colorless so that the symbols are secret until illuminated or they may also be colored so that they can be seen visually. In the latter case, the shape of the symbol is significant, such as a letter or digit. However, the area of the symbol from which luminescence of each coded component present is observed are substantially equal. Preferably the photoluminescent components have a figure of merit, =I equal to where a =average value of the Lambert absorption coefficient a, per cm. of path length, averaged over a continuous wavelength interval of about 15 m which includes, or is included within, the wavelength range used for excitation, and lies at wavelengths longer than about 240 I'll 1.; [Ln]=concentration of the lanthanide ion responsible for the desired luminescence band, in units of moles per liter; =eifective quantum etficiency, namely, the ratio of number of quanta emitted in the luminescence band to be used in the coded ink system to the total number of quanta absorbed in the wavelength range specified for u for the particular active component in the physical condition in which it would appear in the coded ink deposit. .5 should be larger than about 1O I should have, preferably, a minimum value of 200.
The problem of retrieving by rapid mechanical means information encoded on flat or nearly flat surfaces has become of increasing importance in recent years in connection with the widespread automation of certain routine clerical operations. The problem will be briefly illustrated in connection with coded numbers on bank checks, which is an important and well-developed field for such automated readouts. The check on a particular account has printed on it, usually on one edge, a coded number corresponding to that account. Most commonly, the coded number is printed in magnetic ink so that there can be no confusion with other notations in non-magnetic ink which may extend into the code area when a check is made out or is otherwise handled. When the checks are paid, they are run through a scanner which scans the magnetic code and which sorts the checks into different accounts or otherwise retrieves the information as to which account a particular check is drawn on. Such scanning is enormously more rapid than visual examination and, of course, avoids human error. It is, of course, not necessary that the magnetic ink be printed in legible characters, such as numbers; any other symbol which would be picked up by the scanner and correctly interpreted could be used. However, in the bank check field at least, it is common practice to have the magnetic ink pigmented and to use intelligible symbols, so that if the scanner breaks down or if a counter check is made out which has no magnetic printing it can be processed manually using visual examination. Throughout the remainder of this application, recorded information will be used without intending it to be limited to that which can also be discerned by eye, although for many purposes the type of symbol which can be read has advantages just as in the prior art. For certain purposes where it is desired that the information remain secret until machineread, for example, prices on articles in stores, articles such as wearing apparel, where visually discernible symbols would be undesirable, and the like, invisible symbols are needed and as pointed out above, it is an advantage of the present invention that the symbols may be pigmented or clear, formed or irregular.
The prior art methods which are illustrated by the magnetic ink symbols on bank checks present certain problems. In the first place, the check must be precisely oriented as it moves through the scanning mechanism and this presents problems because checks are often issued in books and are torn out when used and edges, therefore, may not always be exact. Furthermore, the surface may not be flat due to rough handling. It is also possible that a portion of a number or letter may be damaged and since the reading by the scanner requires the shape of the character, it will not necessarily read correctly in such a case. These problems have not been so serious as to prevent the use of magnetic ink coding in bank checks, but they, nevertheless, do represent an undesirable factor. There is, therefore, a need for coding processes which are not dependent on exact shape or orientation when scanned.
SUMMARY OF THE INVENTION Essentially the present invention writes, types, stamps, or otherwise produces symbols which are composed of a mixture of chemical compounds, which mixture can be colorless or pigmented, in the latter case permitting symbols which also can be read by the eye. Certain components of the mixture, hereafter termed active components, are substances whose presence (or absence) in the mixture can be recognized, or detected, thereby permitting the establishment of a simple code for the mixture based on the presence (or absence) of various active components, alone or in combination. While the present invention is not limited to the binary system of merely presence or absence of individual active components in the mixture (as contrasted to additional levels of presence), the initial discussion of operation will be in terms of the binary system. When we are dealing with the presence or absence of various active components, the number of combinations of n active components is 2. The one corresponding to the absence of all components, of course, is useful only as a control symbol, for instance to indicate separation of symbols into groups, because there would not be any distinction from the substrate to which the writing material was applied. Four active components, therefore, would permit fifteen distinct combinations, allowing, for example, a one-to-one association with decimal digits and leaving five combinations for assignment as special symbols. Six active components would permit sixty-three distinct combinations, allowing a one-to-one association with, say, the ten decimal digits, the twenty-six letters of the English alphabet, and leaving a number of combinations for other purposes. These writing materials, consisting of mixtures of active components with whatever other substances are needed to provide a satisfactory suspending medium, will hereafter be referred to as coded inks. The singular form, coded ink, will be taken to mean a specific combination of active components. This use of the term ink is not intended to imply the presence of a colored or dark substance in the writing material, but is used in a more general sense as a material which can be transferred to a substrate for recording information.
The present invention can be used in pigmented form so that the symbol will be visually readable, or it can be in completely unpigmented form and without shape, for example, small rectangles which can be colorless if desired. The possibility of using pigmented inks permits all of the advantages of combined visual and machine reading, which has been referred to above in connection with bank checks, but does not carry with it either of the disadvantages. First of all, exact orientation is in no sense necessary, for machine reading is concerned only with the presence or absence of active components in a particular symbol and not at all with its shape. Checks with ragged edges or other materials which do not lend themselves readily to exact orientation in a reading machine are read with complete accuracy, and if there has been a partial destruction of part of a symbol, this does not interfere with accurate machine reading so long as there is any of the symbol left. Thus, two of the definite drawbacks of the prior magnetic ink process are not present. Furthermore, a sequence of symbols can take the form of concentric circles (or polygons), allowing even greater latitude in orientation relative to a reading device. All of these possibilities make the present invention extremely flexible, and it can be used for any of the purposes of earlier processes but without many of their drawbacks.
It is clear that for greatest utility of this invention two elements which must be present are (1) a relatively simple and reliable means for detecting the presence of active components, and (2) four or more active components which are relatively non-interfering with respect to the detection scheme. The manner in which the presence of various active components in a given coded ink are recognized, or detected, in the present invention is by the particular luminescence emitted when the coded ink is illuminated with short wavelength radiation. This luminescence results from excitation of energy levels of the active components and is not to be confused with simple reflection of the exciting radiation. Furthermore, luminescence is here taken to mean the emitted radiation whether it occurs in the visible region of the electromagnetic spectrum or not. For example, it includes X-ray fluorescence in relatively narrow wavelength bands from a component excited by a relatively broad band, so-called white X-rays. The read-out mechanism produces a response, for example, electrical, which determines the presence or absence of each particular active component in the mixture.
It is an important feature of the present invention that the active components are mixed together to form the coded inks, so that the same information is contained in all parts of a symbol formed with a given coded ink. If desired, however, the mixing may actually be accomplished during the writing process on the substrate surface, with the requirement that spatial separation of components be less than the geometrical resolution of the readout mechanism. In fact, the active components can be superimposed in any order, during writing if one so chooses. In some cases, certain active components may be soluble in the ink vehicle, while others of a mixture are not. In this situation, it is possible that some spreading or bleeding of the soluble active components may occur relative to the insoluble active components, but generally conditions will be chosen to render this phenomenon unimportant.
While in its broadest aspect the present invention is not limited to particular luminescent active components, in a more specific and preferred embodiment a certain class of luminescent materials is of predominant practical value, at least for most of the active components. Most organic compounds which exhibit significant photoluminescence fiuoresce over a broad wavelength range (several hundred angstroms) and have an absorption band immediately adjacent and sometimes overlapping the luminescence band on the short wavelength side, the so-called mirror-image situation. This is also the situation for many inorganic luminescers. The width of the fluorescence band and the presence of the accompanying broad absorption band makes the use of more than one or at most three such materials impractical as active components.
In order to avoid these problems of interference between components, the preferred and by far the most practical type of active component is represented by certain complexes of rare earth metal ions having an atomic number greater than 57. These metal ions all belong to the lanthanum group and, therefore, in the claims they will be referred to as lanthanide ions having an atomic number greater than 57, although of course this limitation excludes lanthanum itself. It will be noted that in some of the illustrations compositions are described which contain both lanthanide ions and rare earth ions not belonging to the lanthanum group.
The chemical groups bound to the metal ion generally are referred to as ligands, and this is the terminology which will be employed in the present application. Ligands which in combination with the metal ion exhibit suflicient absorption in the ultraviolet and/or blue region of the electromagnetic spectrum will be termed chromophoric ligands. Preferred complexes are those containing one or more chromophoric ligands, where at least one point of contact between the chromophoric ligand and lanthanide ion is via an atom involved in the chromophoric grouping.
The chromophoric grouping may be largely or completely organic or it may be inorganic. The different types of chromophoric groups have both advantages and disadvantages. The organic groups which contain organic chelating ligands have the advantage that for the most part they are soluble or readily dispersible in ink vehicles to form inks which dry in the form of relatively homogeneous films. However, the stability of the organic chromophoric groupings to conditions tending to degrade them, such as long continued exposure to intense actinic light, is not of the highest. In contrast, for the most part, inorganic chromophoric groupings are highly stable to conditions such as actinic light, against which the organic chromophoric groupings are not so stable. On the other hand, the inorganic chromophoric groupings form compositions which, for the most part, are not soluble in ink vehicles and are not as readily dispersible to form inks which dry to relatively homogeneous films. The choice of the particular luminescent compounds to use can be largely dictated by practical considerations involving the intended use of the coded inks. Thus, for example, if articles are marked with coded inks for sorting and do not have to remain stable underdrastic conditions, such as long exposure to actinic light, the compositions utilizing organic chromophoric groupings will ordinarily be preferred. At the other extreme, where continued exposure to drastic conditions such as strong actinic light, are involved, luminescent materials With inorganic chromophoric groupings present many advantages. Other uses under conditions intermediate between the two extremes referred to above may utilize either type of composition. It is also possible in a single ink to have both organic and inorganic luminescent material, and the present invention may, therefore, use one or other type or both. The fact that the choice of luminescent composition between organic and inorganic can be dictated by practical considerations of use adds a very desirable flexibility to the present invention.
Of particular preference in the organic category are certain groups of organic chelating ligands. A ligand attached to the metal atom by more than one atom in such a manner as to form a heterocyclic ring is said to form a chelate, and the molecule or ion from which the ring is formed is known as a chelating agent or chelating ligand.
The preferred chelating ligands of the present invention belong to the group of betadiketones having the formula -o R1- GH=( JRz wherein R and R are the same or different radicals selected from the group consisting of alkyl of 1-18 carbon atoms, halogenated alkyl of 1-18 carbon atoms (F or Cl), alkoxy of 2-18 carbon atoms, phenyl and sub stituted phenyl, fury] and substituted furyl, thienyl and substituted thienyl, and hetero-aromatic systems.
Another type of chelating ligand is represented by the formula wherein R is an alkyl group of l-18 carbon atoms or a fiuorinated or chlorinated alkyl group of 1-18 carbon atoms, and R through R7 may be the same or different groups selected from hydrogen, an alkyl group containing 1-18 carbon atoms, or a fiuorinated or chlorinated alkyl group of 1-18 carbon atoms.
Denoting the chelating ligand by L, these rare earth metal chelates may be represented by the chemical formulas BML ML ML X, and MLXY, where B is a cation such as Na+, NH (C H )4N+, and piperidinyl, X and Y are anions such as OH and Cl", and M is a rare earth metal ion. Frequently the compounds crystallize with one or two molecules of solvent per formula unit of metal chelate.
Chelating agents which coordinate to the metal ion via atoms other than oxygen also exist. For example, the neutral chromophoric ligand 2,2-bipyridine can form coordinate bonds to a rare earth ion via its two nitrogen atoms, represented by the structural formula where M is a tripositive lanthanide ion of atomic number greater than 57 and X is an anion such as Cl" or N0 or may be a chelating anion such as L.
All of these lanthanide chelates exhibit strong absorption of radiation in the ultraviolet region, characteristic of the chelating ligand. By a process of internal conversion and intersystem crossing some of this absorbed energy is transferred to the rare earth ion, exciting it to a luminescent electronic state. Emission of radiation by the lanthanide ion occurs in rather narrow wavelength bands, 100 A. wide, compared to organic fluorescers. Thus for these lanthanide chelates the absorption characteristics are determined by the chelating ligand, while the wavelength and narrow-band character of the luminescence are determined by the lanthanide ion. Hence it is possible to confine the absorption exhibited by coded inks utilizing these active components to the ultraviolet region of the electromagnetic spectrum, while the luminescence ranges through the visible and into the near infrared region. Furthermore, the narrow-band luminescence exhibited by these components, coupled with the separation of wavelengths at which they luminesce, permits the detection of one in the presence of others with a minimum of interference. As will be shown later in an example, it is possible to use a single common broad band fluorescer as an active component along with these narrow-band luminescent components, provided the broad-band fluorescence falls on the short wavelength side of the primary luminescence bands of the other components. If this condition is not satisfied great care must be taken to ensure that the mirror-image absorption does not interfere.
The quantum efficiency for luminescence, that is, the ratio of the number of photons emitted in luminescence to the number of photons absorbed in excitation, varies considerably for the rare earth chelates, being particularly dependent on the environment. Even the best of the chromophoric ligands have only moderate quantum efficiencies, which is thought to be due to a number of the excited molecules losing energy by different paths which do not result in radiation, and if they could be shielded so that they do not take these paths, increased quantum elficiencies would result. Hydrocarbon radicals are good insulators or shields, but hydrocarbon solvents are not fully effective because the dispersion of individual molecules is not perfect. For the tris chelates, ML it has been found that a number of compounds which have hydrocarbon radicals and a grouping which has covalent affinity for the rare earth ion appear to adhere to the chelates and greatly increase the quantum efiiciency. It should be noted that rare earth ions appear to have a coordination number of eight, or even nine, for oxygen, nitrogen or sulfur atoms. The three chelating ligands occupy six of these sites, leaving two sites vacant. These vacant sites permit the formation of adducts with the above mentioned compounds. Since the phenomenological effect of these compounds is a synergism insofar as luminescence is concerned, they initially were referred to somewhat loosely as synergic agents. For want of a better name, this designation will be used in the present application. The synergic agents include a variety of classes of compounds, namely, the trialkyl Group V-A oxides (where the Group V element is nitrogen, phosphorus, arsenic, antimony and bismuth), alkyl dialkyl phosphinates, dialkyl alkyl phosphonates, trialkyl phosphates, hexa-alkyl phosphoramides, dialkyl sulfoxides, cyclic sulfoxides, cyclic sulfones, dialkyl sulfones, aliphatic esters, aliphatic ketones, cycloalkanones, aliphatic aldehydes, etc. A typical and one of the best synergic agents is a trialkyl phosphine oxide with alkyl groups of 5-12 carbon atoms and, specifically, trioctyl phosphine oxide. The new compositions of the rare earth chelates with the synergic agents, and particularly liquid lasers and plastic media involving such compositions, form the subject matter of the Patent No. 3,377,392, issued Apr. 9, 1968.
In the case of laser operations where very high power levels may be involved, quantum efiiciency is of prime importance. In the present invention, for many uses energy demands are much more modest and, therefore, the use of synergic agents with the rare earth chelates is not as vitally necessary. Nevertheless, higher efliciency is never harmful and so, in a preferred embodiment of the present invention chelates of the lanthanides with synergic agents are included.
Of particular preference in the inorganic chromophore category are halide, chalconide, oxide, and oxyanion ligands, including compositions in which lanthanide complexes may be guests in a non-lanthanide host matrix. The stronger absorption bands associated with these ligands sometimes are called electron transfer or charge transfer bands, implying some relationship to a migration of charge, but the exact mechanism has not been demonstrated unambiguously and it is unimportant in the present context. In certain host lattices it is possible that absorption may occur in chromophoric groups not directly attached to the lanthanide ion which luminesces, with some or all of this energy transferred to the appropriate lanthanide ion system in order to excite luminescence. When such a situation exists, it is obvious that the host lattice with the luminescing moiety constitutes the active component. This active component would then have to be ground to a fine powder for mixing with other active components in formulating coded inks.
Oxyanion ligands include species such as borate, aluminate, silicate, phosphate, sulfate, titanate, vanadate, chromate, arsenate, zirconate, niobate, molybdate, plumbate, stibnate, germanate, gallate, stannate, bismuthate, and tungstate, and derivatives differing from them by changes in valence state. Specific illustrations of possible active components include the compositions Y M VO 1x x 4 l-x x 4, 4)1X( 4)X:
(Y M, O and various borate and silicate glasses doped with appropriate lanthanide oxides and preferably including other chromophores. In the illustrations cited, M is Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, or Yb and x usually is 0.01 to 0.1, but in some cases may be as low as about .001 and as high as about 0.5. These materials are solids at room temperature and are normally ground to fine powders before mixing to formulate the coded inks.
The term lanthanide complex frequently is used to mean a lanthanide ion plus any ions or molecules which are attached to it and which can be regarded as bonded to it, whether by ionic or covalent bonding. It is a general term applicable to all kinds of stable lanthanide compositions, whether the complex exists only in a solid environment or may exist in other phases. For example, in a solid with the composition Y Dy VO there are complexes of dysprosium ions present in the yttrium vanadate lattice. The detailed nature of the dysprosium complexes in this case is determined to a large extent by the host lattice. The spectral intensity contour of the narrow band luminescence is characteristic of the dysprosium complex present, even though some of the excitation may occur via photons absorbed in chromophoric groupings not directly adjacent to the dysprosium ions in the lattice. For a particulate material of this type it is the entire composition of yttrium vanadate host and dysprosium guest which is termed an active component. Because of the intimate relationship of luminescence characteristic to the host-guest arrangement for active components of this type, the entire particulate composition is included within the term lanthanide complex. Other illustrations are provided by the solid phase compositions Ca Tb o.9'1 0.03 4 and o.999s o.0001 1.000i- The theoretical number of potential active components, both with organic and inorganic chromophoric groupings, is, of course, enormous. However, since the present invention is directed to practical compositions, the use to which these compositions are put results in imposing certain limitations. In many of the applications for coded inks, the ink, on drying, will be in thin films, for example of the order of 10 1. in thickness. As a result, the absorption coefficient of the active components should be large enough to absorb sufiicient of the exciting radiation incident upon a thin film couple with adequate quantum efiiciency, as has been referred to above, so that there will be a sufficiently intense luminescence to permit reading the coded inks with adequate reliability, which may be considered in a slightly different aspect as an adequate signal to noise ratio. It is also necessary that the wavelength range over which absorption occurs should be large enough to minimize problems in matching excitation radiation with absorption bands. Many useful ink vehicles are not very transparent at around 250 mu but are more transparent at longer wavelengths. Therefore,
there will be certain useful wavelengths of peak radiation which will not be identical for each ink. It should be understood that the shortwave illumination may be in broad bands, for example the emission from a high pres sure xenon are, or it may be in relatively narrow lines, such as the emission lines of a mercury are.
As the highly purified lanthanide elements used in the present invention are not inexpensive, it is desirable to obtain as many luminescence photons falling within the wavelength band, selected for use in the coded ink system, emitted per lanthanide ion, as possible under conditions of use. Not only must exciting photons reaching the active components be absorbed, but there also must be a reasonable quantum efliciency for emission of the desired narrow band luminescence. A workable criterion for selecting the more practically useful compositions is obtained by incorporating these physical factors in an expression designating a number which may be used as a figure-of-merit for the active components.
Since some of the lanthanide active components can form films that are homogeneous whereas others, such as many of the active components involving inorganic chromophoric groupings, are not soluble and do not form homogeneous films, somewhat different methods for arriving at figures-of-merit will be described for these two situations. As will be pointed out below, parameters are so chosen that the figure-of-merit for both types of active component are comparable for the purpose of selecting components having practical utility.
The absorption of radiation in a homogeneous medium can be represented by Lamberts law,
Where 1/1 is the ratio of intensity after, to that before, passing through the thickness Z, and a is the absorption coefficient. It should be noted that at is a function of Wavelength. Under conditions were active components are used as solutes in a solvent, the concentration can be regulated to give a desired absorption coefficient over a range of values. On the other hand, when the active component consists of a powder to be dispersed in a film, the absorption coefficient within a given particle is fixed, and it is only the particle size and number density of particles in the film which can be varied. The effective absorption of exciting radiation by a heterogeneous film of dispersed particulate matter is not simply and directly related in a quantitative manner to the absorption coefficient of the individual active component particles.
A figure-of-merit, P, for active components in a homogeneous medium is defined by the expression,
where a =average value of the Lambert absorption coefficient a, per cm. of path length, averaged over a continuous wavelength interval of about 15 m which includes, or is included within, the wavelength range used for excitation, and lies at Wavelengths longer than about 240 m [Ln] =concentration of the lanthanide ion responsible for the desired luminescence band, in units of moles per liter; =eifective quantum efiiciency, namely, the ratio of number of quanta emitted in the luminescence band to be used in the coded ink system to the total number of quanta absorbed in thewavelength range specified for x for the particular active component in the physical condition in which it would appear in the coded ink deposit. g Should be larger than about 10*. As several of the factors vary somewhat with temperature, the expressions for figures-of-merit must be at specified temperatures, and in the present application will be determined at 25 C. The wavelengths used for excitation should be selected as representing the best match between intensity maxima in the excitation spectrum and practical excitation sources. Satisfactory excitation sources include xenon arcs and mercury arcs, ranging in power from a few watts to kilowatts.
Data for computing the figure-of-merit, Q, can be obtained in a conventional manner for molecular dispersions of active components in homogeneous media. For the simple lanthanide chelate complexes which follow the Beer-Lambert law, the expression for Q reduces to where e is the molar extinction coefiicient or molar absorbance. For practical utility should be larger than 200, and for the best inks it is preferred that it not be less than 800. At the end of the specification, figures for typical compositions will be given in Table 1, including compositions of some of the examples and also some compositions which had figures of merit, I falling outside of the minimum of 200.
With compositions which do not form homogeneous films, direct measurements of the individual quantities used in calculating 1 usually are not practicable. Therefore, a different and indirect measurement is utilized, leading to a figure-of-merit I which, however, as has been stated above and as will be brought out below, yields a measurement which is substantially equivalent to the Q for active components in homogeneous films. Either '1 or I as the case may be, will distinguish between practically useful lanthanide complexes and those which are not.
The determination of 1 is based on a comparison of the photoluminescence of a special disc containing the potential active component A, with the photoluminescence of a comparable disc designated standard disc, containing an active component about which information is available de-signated as standard luminescer. This standard luminescer consists of small particles of solid polymethylmethacrylate in which the di (trioctyl phosphine oxide) complex of europium tris trifiuoroacetylacetonate, hereafter designated as Eu(TFAC) (TOPO) has been dissolved to a fixed concentration level.
The standard luminescer is prepared by dissolving 0.196 gram of Eu(TFAC) (TOPO) in 700 milliliters of benzene containing 14 grams of polymethylmethacrylate, then freeze-drying the resulting solution with care to exclude moisture, and grinding the resulting solid. The particles thus obtained are fibrous in nature, with a filament diameter of about 2 microns, and consist of clusters about 50 microns on an edge. The absorption coefficient, for these particles has an average value of about 540 cm. at 313 my, and the luminescence band of interest peaking at about 613 III/.0.
A mixture consisting of grams of reflectance standard grade barium sulfate powder and 40 milligrams of standard luminescer is ball milled for fifteen minutes, and the resulting thoroughly mixed powder is placed in apparatus for preparing a pressed powder disc. The apparatus used consists of a piece of stainless steel cylindrical tubing 2 centimeters long, inside diameter 3.5 centimeters and outside diameter 3.8 centimeters, equipped with a plunger. In operation the tubing is set on a clean, finely ground glass plate (with its axis perpendicular to the plate), the powder is placed inside the cylinder, the plunger is inserted on top of the powder, and pressure is applied to the plunger gradually. The force on the plunger is increased to 1000 pounds and then released, the plunger is removed, and the cylinder is removed from the glass plate. A pressed powder disc is contained in the cylinder, and the surface which was in contact with the ground glass surface is termed the front. This particular disc is designated as a standard disc.
An analogous disc for powdered lanthanide luminescer A (ground to a particle size of 2-5 microns) is prepared by the same technique, except that the amount of luminescer added is multiplied by the ratio of densities of luminescer A to standard luminescer. This allows a comparison with equal volumes of luminescer particles in the discs, rendering light scattering differences less important. This disc is referred to as disc A.
The standard disc is illuminated by a steady source of ultraviolet radiation centered at 313 my. and having a half-intensity band width of about 6 111,14, with an intensity, I(E, SD), in terms of quanta per cm. per second, striking the front surface of the disc at an angle of about 40. The intensity of luminescence in the desired band, I(L, SD), is measured in the direction of the outward normal to the front surface of the disc in terms of quanta per cm. per second striking the detector. Then disc A is illuminated with the same geometry, but with the wavelength of excitation selected from the excitation spectrum as described for homogeneous films, and the intensity is designated as I(E, A). Similarly, the intensity of luminescence is measured with the same geometry as before, except the wavelength band selected is the one appropriate to luminescer A in a coded ink system, and it is designated as I(L, A). The alternate figure-of-merit, I then is defined by the expression iuL, SD) ME, A) i 1 where, for the purpose of this invention, K is assigned the value 175. Here [Ln] is the concentration of luminescing lanthanide ion in luminescer A particles in units of moles per liter. It should be noted that the value assigned to K is chosen so that I for an active component in particulate form will have approximately the same range of values as I in the region which separates desirable active components from the poor ones. In other words, the ranges for i namely greater than 200 and preferably greater than about 800, hold true for 1 also. In Table II at the end of the specification, typical compositions which produce heterogeneous films are listed with their values of I including compositions of some of the examples and also several which fall below the acceptable limit for I Typical wavelengths at which luminescence. is observed from rare earth ions are as follows, Pr+ (0.51 or 0.65 Nd+ (0.88 and 1.06 Sm+ (0.645 Eu+ (0.613,u), Tb+ (0543 1), Dy+ (0576a), Yb' (0970p), Er+ (0.52- 0.55 and 1.54 0, Ho (0.54 and Tm+ (0.48 and 08 It will be noted that some of these bands are in the visible, and a few are in the near infrared. Reading heads such as, for example, the one which will be described as an illustration below, can, of course, be provided with detectors of suitable wavelength response. The present invention is, therefore, not limited in its broader aspects to the use of inks which luminesce in the visible region of the electromagnetic spectrum. For applications where invisible symbols are desired, the code may be so arranged that every digit has an active component which luminesces in the visible region, thereby permitting emergency visual examination with an ultraviolet source. It is an advantage of the present invention that it is extremely flexible and can be used in a number of-tways.
Inks are usually provided with some film-forming material so that the symbols do not readily smudge or wash away. The present invention is not concerned with any particular ink formulation apart from its active components, except for treatments which might destroy, wholly or partially, the luminescent characteristics of the active components, and is, therefore, not limited to the particular film-forming agent which will be described below in specific examples.
In addition to the use on bank checks referred to, some other typical uses in connection with sorting, right of access, identification, or general data storage are as follows:
( 1) goods identification and labels (2) personal identification (coded personal effects) (3) identification and registration of passing vehicles (cars, trucks, box cars) (4) machine reading of text for any computer, printing,
or transmission operation (5) ZIP codes (6) reading of invoices, tags, etc.
(7) high capacity data storage devices, e.g., discs It will be noted that some of the uses lend themselves to machine reading whereby a large number of small articles, such as bank checks, are rapidly passed and properly sorted or the information fed to a suitable computer. The signal which is produced by a read-out mechanism in the present invention can, of course, be used for any purpose; and the present invention may be said to cease once a suitable signal has been read out.
In connection with reading invoices, a new possibility is opened. For example, a coded ink system with 10 components permits 1023 unique inks, and hence these individual inks can be used to represent numbers up to 1023. This would permit a store with unit prices of the order of $10 or less to use a one-ink tag or stamp encoded with the price on a given piece of merchandise. Similarly, a one-ink mark or symbol on an article could serve as a key in a fairly complex sorting system.
Writing can be effected in various ways, with a multiplicity of pens, one for each ink, or separate stamps with separate stamp pads, or it is even possible to develop a typewriter which records each character in its own ink. This is somewhat similar to the procedure used in multipoint recorders which print with different colored inks.
Writing also can be effected by stepwise printing of symbols in layers of active components, analogous to conventional color printing but without the rigid alignment requirements. Indeed, the bottom layer might even consist of a normal ink with conventional character symbols, While subsequent layers contain active components in transparent films printed in simple blocks over the conventional characters. In still other printing devices the active components, along with film forming vehicles, may be deposited individually but simultaneously on the substrate surface from a multiplicity of fine orifices.
DESCRIPTION OF THE INVENTION The invention will be described in connection with specific examples in which the parts are by weight and in conjunction with the drawings, in which there is shown, in diagrammatic form, a typical read-out mechanism.
Example 1 225 parts of europium nitrate hexahydrate are dissolved in 10,000 parts of water and the solution buffered to a pH of 7.6 with a phosphate buffer. 327 parts of, 1,1,1,2,2-pentafiuoroheptane-3,S-dione are dissolved in 15,000 parts of ether along with 180 parts of a 3.9% aqueous ammonium hydroxide solution. The solutions are shaken together for one hour at 25 C., the ether phase decanted and the trischelate of europium isolated by drying the ether solution and boiling off the ether. 700 parts of trioctyl phosphine oxide are dissolved in benzene and the europium chelate is added. The amount of benzene is suificient to produce a 2% solution of the europium chelate-trioctyl phosphine oxide complex.
Example 2 The procedure of Example 1 is repeated replacing the europium nitrate with 223 parts of samarium nitrate hexahydrate and replacing the 326 parts of pentafluoroheptane-3,5-dione with 208 parts of symmetrical hexafluoroacetylacetone.
A 10% solution of polymethylmethacrylate in benzene was prepared and divided into 10 parts. To each of these parts the solutions of Examples 1 to 4 were added in accordance with the following code in which P stands for the presence of the chelate and A for 1ts absence:
Eu Sm Tb DPA Code P P P P 0 P P P A 1 P P A P 2 0 P P A A 3 P A P P 4 P A P A 5 P A A P 6 P A A A 7 A P P P 8 A P P A 9 The proportions of solutions of Examples 1 to 4 used were such as to produce comparable effects from the particular type of photosensor described below, a type which Was much more sensitive in the blue region of the spectrum than in the red region. For example, in the system coded as 1 the ratio of europium to terbium to samarium chelates was about 1:4:30. The total amount of chelate was about 1% of the weight of polymethylmethacrylate in the solution. In this fashion ten different coded inks were formulated.
The coded inks thus prepared were used to form rectangular symbols, for example 3 mm. x 5 mm., on plain nonfiuorescent white paper, a different ink being used for each symbol. Let us assume that ten symbols are formed, so that each ink is used, and hence all the decimal digits of our code are represented. Under normal illumination all symbols had the same visual appearance, namely a thin rectangular plastic film adhering to the surface of the paper.
The coded symbols are then passed under a reading head as shown in the drawing, the white paper surface being indicated at 12. The reading head is provided with a photon source 2 containing an ultraviolet transmitting visible absorbing filter in its envelope. Each rectangle of different ink is shown by short dashes on the surface 12. Each rectangle when illuminated by the ultraviolet emits radiation of wavelengths corresponding to the presence of the different luminescent active components. The samarium chelate produces red radiation, the europium chelate orange-red, the terbium chelate green, and the organic fluorescent substance, namely diphenylanthracene, blue. As each rectangle passes under the middle of the reading head, it is imaged by lenses 3 onto an aperture 4, and the beam from this aperture in turn is collimated by lens 5, and the beam thus produced passes through a dispersing element, diagrammatically represented by a prism 6, and each of the dispersed wavelength bands are imaged by lens 7 on particular phototubes 8, 9, 10, and 11. The particular colored beams are shown in arrows and are marked with letters R, O, G, and B respectively for the samarium chelate, europium chelate, terbium chelate, and diphenylnthracene emission bands respectively.
Each phototube receives only one wavelength band and, therefore, produces a signal only if that particular wavelength is emitted. The ten different inks shown in the table above produce ten different signals, each one unique for a given coded ink. The signals are then used in any suitable manner, for example, they may be fed into a computer or fed into an automatic sorting machine. These signals may easily be obtained as electrical signals and connected to conventional electronic devices. As has been pointed out above, the present invention is not concerned with the particular use to which the different signals are put. In other words, the present invention ceases once a signal has been produced which uniquely corresponds to a particular coded ink.
It should be noted that the'code described in detail above has been essentially a binary digital operation, that is to say, a component is either present or absent. Combined with the narrow-band luminescence characteristics of the active components, this provides a very high signal to noise ratio and provides for accuracy which cannot be approached by scanning or reading means in which shapes of characters are involved. Where the number of coded inks is not too large, and this depends on the number of narrow-band luminescent components available, the binary coding procedure illustrated above has advantages and gives the highest possible accuracy even in unfavorable environments.
In more favorable environments the use of varying concentrations, which has been briefly referred to above,
permits an enormous increase in code complexity with only moderate decrease in absolute independence from interference. For example, let us consider the situation where each component may be present in one of two concentrations, for example, bearing the ratio of 2 to 1, or be absent. This is now a ternary operation and so the number of coded inks is no longer 2 -l but 3 -1. Four components-now would permit 80 different coded inks which would accommodate all decimal digits and English letters with a number of additional coded inks for other purposes. In other words, this with four components would permit more different coded inks than in the binary system with six components.
If a ternary system is used, there would still be only four detectors but they would be followed by at least one electronic circuit element which responded to one of three different signal levels instead of only presence or absence of signal. Such circuit elements are completely conventional, inexpensive and reliable. Of course, there is not quite the absolute enormous lack of response to spurious signals as in the binary system, but with three levels of signal the discrimination against spurious signals is still so great that for a large number of uses there is no significant difference in accuracy and reliability.
While the present invention requires a readout which will give signals depending on the presense or absence, or also different levels of presence, of each active component, the readout illustrated in the drawings is only a typical one for use with thin moving surfaces such as checks, envelopes, tapes, manuscripts, and the like. Various modifications can be described, with certain configurations having advantages for special situations.
The reading head illustrated provides for ultraviolet illumination over a rather large surface area, coupled with optical isolation of a small area from which luminescence is detected. Conversely a reading head can be designed which provides for ultraviolet illumination of a small surface area, coupled with a luminescence optical detection system which isolates essentially the same section of surface, or a somewhat larger area which includes the ultraviolet illuminated area. Indeed, using a well collimated, or well focussed, ultraviolet beam, such as that from an ultraviolet laser, it is feasible to scan a sequence of coded ink symbols on a fixed surface in turn merely by rotating the ultraviolet source or by using an oscillating mirror or its equivalent. Combining this scanning feature with detection optics viewing the area scanned by the ultraviolet beam, signals are obtained from the photodetectors at a given time which correspond to the particular coded ink symbol being illuminated by the ulttraviolet beam at that time. Broadly, therefore, the ultraviolet source is not restricted to a fixed configuration relative to the photodetecting unit. Furthermore, the ultraviolet or other high energy photon source may provide radiation of constant intensity with respect to time, it may oscillate with respect to time, or it may provide pulses of radiation. In the latter two cases provision must be made in the photodetecaion unit, or in the associated electronic components, for this time dependent excitation. In cases where an ultraviolet transmitting substrate is used, it is possible and even sometimes desirable to illuminate the symbol from the back side relative to the detector viewing side. While the ultraviolet source always performs the function of photo-exciting the active component to develop characteristic luminescence, as in the illustrated reading head, the different physical forms are engineering details and, as such, do not necessarily form part of the present invention which is, therefore, not limited to a particular type of reading head.
Separation of the various radiation bands has been shown in the form of a dispersing element, such as. a prism for which of course a grating could be substituted. In other words, the device is a very simplified spectrometer. For some purposes this presents considerable advantages as it is very flexible and permits quite precise separation of different fluorescent radiations. For other purposes, however, it is sometimes more economical to use narrow band-pass filters in front of the different detectors. In still other cases dichroic mirrors can be used, and all of these approaches can be used alone, or jointly with each other, in combination with the wavelength sensitivity characteristics of photodetectors to achieve wavelength sensitive radiation sensing. Again, the invention is concerned with the performing of a series of steps or with broad means for so doing and not with the particular details of the equipment elements.
Phototubes, which can if necessary be photomultiplier tubes, are illustrated in the drawing. For many purposes these highly sensitive devices have advantages. However, again the exact design of radiation detector is not the essence of the present invention and solid state radiation detectors, such as various photoconductors or photovoltaic may be used. For example, cadmium sulphide or selenide cells may be used where the radiation is suitable for them. With some of the chelates, such as those containing ytterbium and erbium, the radiation is in the near infrared and solid state detectors are sometimes more convenient in such cases. Also, solid state detectors are very rugged and somewhat smaller and lighter than tubes. The choice of detector is dictated not by the present invention but by a balance of convenience, taking into consideration the various factors. It is a definite advantage of the present invention that it is extremely flexible and permits the use of a wide range of apparatus elements which are well-known and which permit the choice of the best components for any particular operation.
The preceding examples illustrate typical rare earth chelates with ligands of the 18 diketone type. They give excellent results and may be considered as the preferred type for the present invention. However, the orthohydroxy aromatic ketone ligands are also useful and two typical members are shown in the following examples.
Example 6 260 parts of anhydrous europium chloride are dissolved in 10,000 parts of absolute ethanol, and 500 parts of ortho-hydroxy-acetophenone are added to the solution. This mixture is cooled to 0 C., and then stirred while anhydrous ammonia gas is bubbled through for thirty minutes, allowing the temperature to rise gradually to 30 C. After standing for thirty minutes at 30 C. the solution is shaken with cold petroleum ether to remove unreacted ligand. Nitrogen is bubbled through the ethanol phase for ten minutes, and then the ethanol phase is diluted with an equal volume of cold water. The europium tris chelate of orthohydroxyacetophenone pre- 15 cipitates as a yellow solid. After drying this solid is dissolved in benzene solution containing 1000 parts of tributyl phosphate. This chelate luminesces at the same wavelengths as in the case of Example 1.
Example 7 350 parts of europium nitrate hexahydrate and 164 parts of 2-hydroxy-4,S-dimethylacetophenone are dissolved in 5000 parts of absolute ethanol, and the solution is refluxed for ten minutes. Then 80 parts of sodium bicarbonate are added to the mixture, and refluxing is continued for sixteen hours. The reaction mixture is cooled to room temperature and filtered, and the filtrate is evaporated to dryness, yielding a yellow powder. This powder is extracted with petroleum ether, leaving yellow crystals having the composition Eu(C H O (OH), or EuL (OH), where L represents the hydroxydimethylaeetophenone anion. The crystals are dissolved in a benzene solution containing 550 parts of dihexyl sulfoxide. The chelate luminesces at the same wavelengths as in the case of Example 1.
Example 8 Yttrium oxide (215 parts) was mixed thoroughly with 19.3 parts thulium oxide and 117 parts ammonium metavandate, and the resulting mixture was placed in a platinum crucible and ignited in air at 800 C. for two hours. The product has the composition Y Tm VO and appears to be a single phase. After grinding to break up the larger aggregates, microscopic examination showed the powder to consist of crystals about 2-3 microns on an edge, grouped together in clusters of 210, with an average particle size of about 8 microns. When illuminated with 3100 A. radiation the powder luminesced strongly at 0.48 t and 080a. The luminescence lifetime was found to be 62 microseconds.
Example 9 The procedure of Example 8 was repeated replacing the thulium oxide by 19.1 parts of erbium oxide. The resulting product has the composition Y Er VO When illuminated with 3100 A. radiation the powder luminesced green, with many narrow lines between 0.52 and 0.56 The luminescence lifetime was 11 microseconds.
Example 10 Dry Y O (99.999%), dry Dy O (99.9%), and dry NH VO (99.4%) were mixed together in the weight ratios 22,446/224/23,396, crushed on agate to average particle size of -1 micron, then roll-mixed for 2 hours. The mixture was fired in a platinum vessel at 815110 C. for 55 minutes. Half of the sample was then removed with no further treatment, while the other half was fired 10 more minutes, then annealed at 180il C. for one hour. The product, Y Dy VO has an average particle size of 34 microns when unannealed and 56 microns when annealed.
Example 11 Dry Y O (99.999%), dry Eu O (99.99%) and dry NH VO (99.4%) were mixed together in the weight ratios 21,452/1,760/23,396, ground on agate to an average particle size of 3 microns, and roll-mixed for 2 hours. The mixture was placed in a platinum container, fired for one hour at 725 :10 C., and cooled to room temperture in minutes. The product was crushed and then refired at 725 for another hour. The Y Eu VO so produced was a homogeneous powder with an average particle size of 2 microns.
Example 12 Dry Eu O (99.99%) and dry H WO (99.0%) were mixed in the weight ratio 3,519/7,498, ground on agate to a particle size of -2 microns, and roll-mixed for one hour. The mixture was placed in a platinum container,
16 fired for one hour at 1000il5 C., and then cooled to room temperature over a period of 3 hours. The Eu (WO so produced was a homogeneous powder with an average particle size of about 1;.
Example 13 The procedure of Example 12 was repeated except that the Eu O was replaced by Tb O and the weight ratio of Tb407 to H WO was 3,758/7,498. The Tb (WO thus produced was a white powder.
Example 14 The procedure of Example 11 was repeated except that B11 0 was replaced by Yb O and the weight ratios of Y O /Yb O /NH VO were 2,145/197/2,340. The product thus produced luminesced at 0.985 when excited by 3100 A. radiation.
1 Luminescent component as solute in the vehicle indicated, in the concentration range 10' to 10- molar. Abbreviations used are TFAC: trifluoroacetylacetonate; TOPO=trioctylphosphine oxide; HFAC= l1exafluroracetylacetonate; DPM= dipivaloymethide; TTA=thenoyltrifiuoroacetonate; DBM dibenzoylmenthide; BAG benzoylacetonate; Pip=piperidinyl cation, and BIFAO benzoyltrifluoroacctonate.
2 Wavelength of band maximum in millimicrons.
3 Abbreviations used are PMMA=polymethlymethacrylate solid;
ETAc=ethyl acetate, and alchol=3/1 ethanol-methanol mixtures.
TABLE II Excitation 2 Luminescence 2 Luminescent 1 Component Wavelength Wavelength 1 0.o94 yo .00fl 4 313 575 7, 050 Y .u7El1u.n3VO4 313 618 1, 800 EllVO4 313 618 20 Eu2(WO4)3 r. 254 615 20 254 012 475 313 613 313 545 20 254 545 20 Luminescent component present as solid particles of the indicated composition. Abbreviations the same as in Table 2 Wavelength of band maximum in millimicrons. The half intensity bandwidth for excitation was about 5 millimicrons.
The invention is not limited tou se on thin, flat objects such as bank checks which have been described as one typical example. On the contrary, it is an advantage of the invention that it is equally applicable to articles which may have rough surfaces and which are not fiat such as, for example, sacks of materials such as potatoes, cement and the like.
1. A process of recording information and retrieval of the same which comprises:
(a) writing different coded symbols, each symbol constituting an area coated with at least one luminescent component, and some symbols containing more than ane luminescent component, in admixture over at least some portion of the area of the symbol, the presence or absence of the various luminescent components in a'given symbol being at least a part of the code associated with the symbol, and each luminescent component on illumination with short wavelength radiation, luminescing in at least one wavelength band substantially different from that of any other luminescent component used, this band functioning as an identifier band for the prosence of the component, at least one of the luminescent components being a complex of a lanthanide ion having an atomic number greater than 57, which if present 17 in a homogeneous medium has a figure-of-merit, I defined by the expression where oc is the average value of the Lambert absorption coefficient a, per centimeter of path length, averaged over a continuous Wavelength interval of 15 m which includes the wavelengths used for excitation, [Ln] is the concentration of lanthanide ion responsible for the desired luminescence band, in units of moles per liter, and .2 is the effective quantum efficiency for luminescence in the identifier band when excited by radiation in the wavelength range corresponding to a and which if present in the particulate state, has a figure-of-merit, 1 defined by the expression I(L, A) I(E, SD) I(L, SD) I(E, A)
where SD designates a standard disc of reflectance grade barium sulfate having uniformly dispersed therein 0.4 weight percent of finely divided polymethylmethacrylate containing 0.01 M europium tris trifluoroacetylacetonate di trioctylphosphine oxide in solid solution, A refers to a similar disc of reflectance grade barium sulfate having uniformly distributed therein a volume of the finely divided particulate luminescent component equal to the volume of polymethylmethacrylate in the standard disc, relative to the volume of barium sulfate, I(L, SD) is the intensity of luminescence from the standard disc in the wavelength band peaking at about 613 mp. when it is subjected to 313 III/L radiation with the intensity I(E, SD), I(L, A) is the intensity of luminescence in the identifier band for the particulate component in A when it is subjected to radiation within its excitation band with the intensity I(E, A), and [Ln] is the concentration of luminescent lanthanide ion in the particulate lumiescer particles in units of moles per liter, this figure of merit, I or 1 as the case may be, being at least 200,
(b) illuminating the symbols with short wavelength radiation, spectrally analyzing luminescence from each symbol with radiation detectors responsive, respectively, to a luminescence band from one luminescent component of the symbol and substantially unresponsive to luminescence bands from any other luminescent components in the symbol, the area of each symbol from which luminescence of each component is detected by the radiation detectors being substantially equal and sufficiently large so that the luminescence from each component has an intensity permitting accurate detection, and
(c) transforming the signals from the radiation detectors into a signal uniquely corresponding to the coded symbol.
2. A process according to claim 1 in which I or Q,
as the case may be, is not less than 800.
3. A process according to claim 2 in which the presence or absence of the various luminescent components in a given symbol constitutes the whole of the code.
4. A process according to claim 1 in which the complex is a chelate of the lanthanide ion and at least one chelating agent.
5. A process according to claim 4 in which the presence or absence of the various luminescent components in a given symbol constitutes the whole of the code.
6. A process according to claim 4 in which a chelating ligand is a beta diketone.
7. A process according to claim 6 in which the chelating ligand is 1,1,1,2,2-pentafiuoroheptane-3,5-dione.
8. A process according to claim 6 in which one luminescent component is a chelate of europium and 1,1,1,2,2- pentafluoroheptane-3,5-dione, one luminescent component is a chelate of terbium with the same ligand, one luminescent component is a chelate of Samarium with symmetrical hexafiuoroacetylacetone, and one luminescent component is a chelate of dysprosium with dipivaloylmethane.
9. A process according to claim 4 in which the lanthanide chelate is associated with a synergic agent selected from the group consisting of trialkyl Group V-A oxide, alkyl dialkyl phosphinates, dialkyl alkyl phosphonates, trialkyl phosphates, hexa-alkyl phosphoramide, dialkylamides, dialkyl sulfoxides, cyclic sulfoxides, cyclic sulfones, dialkyl sulfones, aliphatic esters, aliphatic ketoncs containing at least 4 carbon atoms, cycloalkanones, and aliphatic aldehydes, and their thioanalogs.
10. A process according to claim 1 in which the inorganic complex consists essentially of the composition Y M VO where M is selected from the group consisting of Nd, Srn, Eu, Dy, Ho, Er, Tm, Yb, and x has a value between 0.001 and 0.10.
11. A process according to claim 1 in which the message is on moving vehicles.
12. A process according to claim 1 in which the messages are on individual articles which are successively illuminated.
13. A process according to claim 1 in which at least one of the luminescent components is present in more tha one concentration, the concentrations being widely separated.
14. A process according to claim 1 in which the presence or absence of the various luminescent components in a given symbol constitutes the whole of the code.
References Cited UNITED STATES PATENTS 2,957,079 10/1960 Edholm 250-53 3,059,112 10/1962 Rogal 250-71 RALPH G. NILSON, Primary Examiner A. L. BIRCH, Assistant Examiner US. Cl. X.R.
PO-IQSO UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 1 4736091 Dated Ogtober 14, 1969 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 5, line 45 for "ligand" read ligand anion Column 6, line 62 for "5,577,592" read 5,577,292 Column 8, line 70 for "g read Column 9, line 1 for "g read Column 9, line 17 for "g read Column 12, line 20 delete "O" at extreme right of line Column 14, line 6 for "photodetecaion" read photodeteotion Column 14, line 12 for "component" read components Column 16, line 56 for "EI'Ac" read EtAc Column 16, line 50 for "tou se" read to use Column 16, line 65 (Claim 1) for "ane" read one Column 16, line '72 for "presence" read presence SIGNED AND SEALED JUL 2 1970 1SEAL) Attest;
Edward M. Fletcher, Jr. Attesting Officer WILLIAM E. 'SCHUYLER, JR. Commissioner of Patents